1. Field of the Invention
The present invention relates to a method and an apparatus for sanitizing minced meat.
The term "minced meat" is understood to designate a product obtained from the mincing or grinding of meat from the forequarter of bovines, as specified by Directive 84/c 255/09 of the Council of the European Economic Community.
2. Description of the Prior Art
The mincing and reconstitution of meat in the form of "hamburgers" allows quick cooking and increases consumption considerably. However, during mincing, the meat undergoes a temperature increase which facilitates the development of bacteria, especially if strict and perfect cleaning of the mincer is not performed.
Minced meat has an extremely large surface exposed to the air; this causes the development of a brown color of the product due to the forming of oxymyoglobin and danger of microbial proliferation and contamination by germs in the environment and germs introduced by handling, tools, et cetera.
It is known that E. coli 0157:H7 has a growth temperature range of 7 to 50.degree. C. with an optimum level around 37.degree. C.
Other bacteria grow, in air, at temperatures in the range of 10-45.degree. C., with an optimal growth interval at 30-40.degree. C.
Accordingly, heating the meat produces an increase in the bacterial population which can raise its level to values dangerous for the consumer's health (E. Coli can cause gastroenteritis with complications involving the renal function in children and elderly people).
Although modern processing methods, with the use of meat at low temperature (around 0.degree. C.), and laboratories conditioned at temperatures as low as -12.degree. C. have reduced the drawbacks described above, the bacteria presence as reflected by the total plate count (TPC) is still rather high and causes accidents which are very dangerous and sometimes even fatal.
The fact that many countries have set limits for the microbiological acceptability of hamburgers in order to protect both the producer and the consumer demonstrates that the such a food product contamination is still a widespread problem.
To prevent these contaminations, it is known in the art to subject the food products to a heat treatment, such as pasteurization or sterilization and subsequently to deep-freezing and/or to vacuum/aseptic packing. It is usually used the so-called HTST-process (High Temperature Short Time), i.e. heat treatment at high temperature for a short time (see U.S. Pat. No. 5,374,437). The HTST technique is known to limitedly affect the taste quality of a treated food product. However, it only acts at the surface of the product while still producing an organoleptic degradation thereof which consists in a changing of its colour, i.e. the meat has no longer the fresh, raw meat, red colour. This creates the impression of a product which is no longer in the fresh state and, as such, is not appreciated by the consumer.
Moreover, the inner parts of the product are not treated adequately, and this is critical especially in the case of minced meat.
Also known is the use of the ionizing radiation, which sterilizes the meat while keeping it red; however, such radiation is believed to be mutagenic and therefor can cause health problems. Legislation in many countries, in fact, requires to specify on the product if it was treated by ionizing radiations. All this was also seen to negatively influence the consumer at least in that it led to important drops in the consumption of the so treated food products.
Studies have been undertaken to determine the destruction of Escherichia coli 0157:H7 in food systems by microwaves, which are known to heat the inner parts of a product (Czechowitz, S. M., Thesis publ. 1996, University of Minnesota, St. Paul, USA.). It was established that heating of ground beef patties at 67.8.degree. C. in microwave ovens would destroy E. coli. Power levels of microwave ovens were also found to be critical to bacteria lethality (Czechowitz, S. M. and Zottola, E. A.--Institute of Food Technologists, U.S.A. 1996 Annual Meeting).
Attempts have been also made to achieve a heat treatment of the products by subjecting them to controlled heating by microwaves and/or other heating means with the purpose of obtaining, as much as possible, a uniform heating of the whole treated mass (U.S. Pat. Nos. 3,494,723; 3,494,724; 3,809,844; 3,814,889; and 5,308,629)
The disclosed methods and systems, however appear not to be entirely satisfactory being either complicated, adapted for products with limited thickness, not entirely efficient for assuring a uniform temperature all throughout the treatment mass, and eventually conducting to unsuitable and easily perceivable oraganoleptic changes of the treated food product.
Moreover the products treated in accordance with the known methods may undergo significant weight reduction due to water evaporation and fat melting, which is generally commercially unprofitable.